Bearings are needed in any machine employing a rotating member such as a shaft or thrust runner. They provide a stabilizing force, by providing damping or balancing forces on the rotating member of the machine during operation. Conventional roller and ball bearings have generally been used to provide these stabilizing functions needed during the operation of, for example, a high-speed machine such as a gas turbine engine. Air bearings present a desirable alternative to these conventional bearings, because they eliminate undesirable vibration resulting from the presence of the bearings within the machine, and they are maintenance free.
U.S. Pat. No. 4,950,089 to Jones discloses a compliant foil bearing comprising a relatively thin bearing foil that is supported in juxtaposed relation to both a shaft and a bearing housing by a pair of sinusoidally folded spacer foils. A single bearing foil is hydrodynamically spaced from and related to both the bearing housing and the shaft. In addition, the patent states that the spacer elements provide for radial deflection of the bearing foil in accordance with the pressure profile of the hydrodynamic gas film so as to provide maximum load carrying capacity, to tolerate bearing misalignment and skew loads, and to tolerate thermal distortions.
U.S. Pat. No. 4,415,281 to Agrawal discloses a hydrodynamic fluid film bearing including a stationary retaining member, a rotating member and a foil element therebetween. The bearing includes a resilient backing member which has a bilinear spring constant associated with it, adjacent the foil element. The spring is of periodic shape and comprises a first and a second series of corrugations, wherein the amplitude of the second corrugation is substantially less than that of the first corrugations. The bearing is said to achieve enhanced damping with minimum power loss at all speeds of operation as well as improved load capacity, and resistance to rotating member excursions and instabilities due to shaft imbalances and other disturbances.
U.S. Pat. No. 4,552,466 to Warren discloses an air bearing structure which is said to prevent destructive bending moments within the top foil. A top foil member is supported by a bump foil made from Inconel X-750. The bumps are formed by a curved die in an annealed condition.
U.S. Pat. No. 4,462,700 to Agrawal discloses a hydrodynamic fluid film thrust bearing including a stationary thrust plate, and a rotating thrust runner spaced therefrom. A set of corrugated springs is disposed between the thrust runner and the thrust plate.
U.S. Pat. No. 4,295,689 to Licht discloses a fluid-film journal bearing which includes a resilient foil insert assembly mounted in the bore of a retaining member and having a bearing surface of a rotatable journal. The retaining member has a slit extending tangential to the bore with associated means for retaining the foil and for varying the bearing clearance. The foil is coiled within the annular space between the retainer and the journal and is comprised of three integral sections comprising an outermost plain portion, an intermediate undulated or wave portion, and a plain inner portion. The wave portion is formed in the shape of successive, undulating curves having alternating peaks and valleys. The patent states that it is possible to fabricate an almost infinite variety of forms for the wave portion by changing the wavelength .LAMBDA., the peak-to-peak amplitude A and/or the local radius of curvature R.sub.(s), where s is the distance along the undulation, which enables one to vary the stiffness of the resilient backing and the damping of the foil element.
Plastic air bearings have been made by KMC, Inc., of Newport, R.I. These were machined to provide thickness variations and are not believed to have been capable of the "oil-canning" function.
While the need for air bearings exists, they are difficult to make and no method known provides an inexpensive, efficient and cost effective way of producing them. Consequently, their use has been very limited for applications which require tight tolerances, such as precision gauging and precision machines.